The invention relates to an anti-resonant suspension device for a helicopter consisting of a fuselage, a propulsion unit, a rotor and a transmission box located between said unit and said rotor and aligned with the axis of rotation of the latter, this device comprising a suspension plate which is located substantially in a plane perpendicular to the axis of the rotor and the central part of which is fastened to the bottom of the transmission box, and a set of at least three supporting parts, the upper ends of which are connected to the transmission box and the lower ends of which are articulated to the outer ends of arms arranged radially round the base of the transmission box to which they are connected, as well as being connected, in the region of their outer ends, to the fuselage at a strong point of the latter; the various connections of each radial arm allow it to experience deflections as a result of deformation in the radial plane (that is to say, passing through the axis of the rotor) which contains it, whilst these deflections impart substantial movements to a swinging weight mounted at the end of a rigid support, the other end of which is fastened to the end of the corresponding radial arm.